<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button id="btn">按钮</button>
    <script>
        var btn = document.getElementById("btn");
        btn.onclick = function () {
            // console.log(this)
            // setTimeout(function(){
            //     console.log(this)
            // },100)
            setTimeout(() => {
                console.log(this)
            })
        }
    </script>
</body>

</html>